It is well known to operate a blowout preventer having a two-way hydraulic piston and cylinder assembly including an open and close port by means of a control valve connected to a hydraulic supply. However, it is sometimes desirable or even necessary to provide greater closing forces, particularly in the case of shear ram type blowout preventers where the rams must cut and sever pipe in a well. For example, normally some types of blowout preventers may be operated at 1500 psi. However, to insure that shear rams will positively cut through pipe they may require as much as 5000 psi operating pressure.
The present invention is directed to a hydraulic control circuit and method for operating a blowout preventer by boosting the pressure above that provided by the normal supply pressure.